Carbon-13 NMR investigation of local dynamics in bulk polymers at temperatures well above the glass-transition temperature. IV: Polyisobutylene

Carbon-13 spin-lattice relaxation time measurements have been performed at two experimental frequencies on the considered polymer in solution and in the bulk state at temperature well above the glass-transition temperature. The data have been analyzed by using the orientation autocorrelation functions developed for polymers and a modified function proposed for poly(vinyl methyl ether) previously. As observed in the latter compound and other polymers, a fast motion of the internuclear vector must be considered. It can be assigned to librations of limited but significant extent about the rest position. Moreover, the temperature dependence of the segmental motions in bulk polyisobutylene can be understood by considering both glass-transition and secondary relaxation processes. Graphs. 30 ref.--AA